ST. LOUIS – Mayor Bloomberg has some advice for Police Commissioner Ray Kelly: If you’re wondering whether to run for City Hall in 2009, get rid of the doubt and go for it.

Bloomberg described the city’s top cop as a “phenomenally competent guy” but said the two have never discussed Kelly’s possible entry into the political arena.

The Post reported yesterday that Kelly had a meeting with GOP consultant Scott Reed earlier this year leading to speculation that the commish may jump into the 2009 race. Kelly has ducked questions on whether he will run.

“If he asked my advice I’d give it to him,” Bloomberg said after the Urban League’s annual conference here. And what would that advice be?

“I think it’s a great job, and if you want it and you’re willing to go through what it takes to present yourself to the public, stand the scrutiny of the press, you take the shot.”

The mayor said he’d offer the same counsel to anyone, because “you never want to go through life” wondering what might have been.

The choice is a little tougher for Kelly. He’d have to step down as police commissioner once he became seriously involved in politics.

Meanwhile, a Quinnipiac poll released yesterday shows that Kelly’s approval rating is bouncing back after taking a hit in the wake of the Sean Bell shooting.

Some 64 percent of voters approve of his job performance. Blacks give him a 49 percent approval rating, Hispanics give him 57 percent, and Republicans’ approval is at 80 percent.

Kelly fares better in approval ratings than any of the other potential candidates to replace Bloomberg.